1. Field of the Invention
This invention relates to an apparatus and method for high speed data transfer between PCB boards using ribbon cable.
2. Description of the Prior Art
There are several standards for ribbon cable interconnection known today. Three of the most advanced systems are Ultra ATA-66, ULTRA-2 SCSI and Wide ULTRA-2 SCSI. The Ultra ATA-66 standard allows data transfer at up to 66.6 MB/s burst data transfer rate at 33 MHz clock rate over 80 conductor wire using 40 signal and 40 interleaving ground conductors with 40 receptacle connectors. The ULTRA-2 SCSI and Wide ULTRA-2 SCSI allow burst data transmission of 40 and 80 MB/s at 40 MHz. with 8 bit and 16 bit buses respectively. ULTRA-3 SCSI promises double the Wide ULTRA-2 SCSI rates. However, the ULTRA-2 SCSI and ULTRA-3 SCSI systems require the use of twisted pair ribbon cables to support Low Voltage Differential where each signal is sent over two wires. Also the SCSI systems require complex active terminators and utilize data verification techniques such as CRC, which have substantial overhead and which limit the techniques where direct isochronous transfer is required.
High frequency board-to-board data transmission by ribbon cable is limited by issues of signal integrity including the following: a. driver characteristics such as slew rates, propagation delay and signal reflection; b. transmission line effects such as signal reflection impact, termination methodology, incident wave switching, load configurations, connectors, and ribbon cables; c. receiver capabilities, such as thresholds, signal skews, setup/hold times, and loading; and d. cross talk, involving the ribbon cable, signal pin-out, PCB traces, and EMI considerations. All of these factors make it uncertain whether a high speed data transmission over a given ribbon cable connection can maintain data integrity.
Many data transfer systems require both high speed and high bandwidth transfer. One particular system is high performance video transfer. The Video Electronics Standards Association (VESA) has recently adopted Version 2.0 of a Video Interface Port (VIP) Standard, which is a dedicated physical connection between a graphics adapter (a VIP master) and video devices such as MPEG-2 or HDTV decoders, video digitizers, video encoders, etc. (a VIP slave). Such high performance video transfer systems as VIP require reliable data transfer, which is isochronous (real time) and very high bandwidth (VIP 2.0 requires 150 MB/s transfer rate). Because of the limitations on reliability of high speed ribbon cable connections VESA did not adopt a ribbon cable implementation of its VIP 2.0 standard which operates with up to a clock rate of 80 MHz, and contemplates that the standard will be implemented by both master and slave mounted on a single board or a mother-daughter board arrangement. The earlier VIP version 1.1, which operated at 33 MHz included a ribbon cable transfer option. The single board requirement of VIP 2.0 is a significant limitation, since graphic controllers and video devices are typically manufactured by different manufacturers. The objective of the VIP Standard was to assure that devices manufactured by different parties could interface seamlessly. This objective is substantially compromised by the single board requirement.
Other PC based systems for real-time video transfer are not adequate for connecting VIP 2.0 slaves and masters. IEEE 1394 (known as Fire Wire) is isochronous but does not provide high enough transfer rates, USB is likewise too slow for high performance video. Fast PC bus structures such as PCI and AGP are asynchronous buses and cannot provide the needed direct isochronous interconnect.
There is a need for a reliable board-to-board data transfer system for transfer of data above 40 MHz based on readily available and inexpensive components comprising single-ended nbbon cable and connectors, whereby high speed data generated on a slave board constructed according to the system can reliably transfer the data to a master constructed according to the system by a ribbon cable of the system without the signal integrity reliability issues.
There is a need for an inexpensive and reliable system for direct linkage of VESA VIP 2.0 master and slave devices mounted on different boards.
There is a need for an inexpensive and reliable system for direct ribbon cable linkage of VESA VIP 2.0 master and slave devices mounted on different boards such that a board containing a slave of the system will reliably and isochronously link with a master of the system by a cable of the system.
There is a need for a reliable method for data transfer between boards at greater than 40 MHz using inexpensive and readily available single-ended ribbon cable.